The current frequency is expressed in field 310 and in Fixed-length field 008/18 "FREQ." The regularity of issuance is expressed in fixed field 008/19. CONSER practice is to record the frequency using the terminology as provided in the Fixed-length field list of frequency designations unless the stated or actual frequency does not appear in the list.
Take information about the frequency from any source (RDA 2.17.12.2), either from information found in the piece or supplied by the publisher or from evidence of issues already published. If there is no stated frequency, give the probable frequency when there is sufficient evidence to indicate the publishing pattern. Do not use a question mark. If the frequency is unknown, omit field 310 and code the fixed field bytes as "u/u". (CCM: 13.3.2)
Sometimes the frequency requires further explanation to account for stated irregularities in the publishing pattern. Such information is generally taken from the piece but may also be supplied and is given in parentheses following the frequency.
310 ## $a Monthly (except July-Aug.)
310 ## $a Eight times per year
However, the list of frequency designations does not include all possible frequencies. When a serial is issued according to a frequency not on the list, construct a frequency statement using terms such as "... no. a year" or "... issues a year."
310 ## $a Four no. a year {Denotes the issues are numbered and could be combined}
310 ## $a Four times a year {Denotes the serial is issued in 4 separate issues not combined)
310 ## $a Four issues a year Denotes the serial is issued in 4 separate issues not combined)